Blood transports nutrients, oxygen, waste materials, hormones, proteins that need to be redistributed in the body and clotting factors. Oxygen bound to hemoglobin is transported via red blood cells. After the oxygen has been used in metabolism, blood transports carbon dioxide back to the lungs.
There are various methods for transporting different molecules in the blood stream. Oxygen is transported in red blood cells. Carbon dioxide is often transported in the form of bicarbonate and is usually not bound to any particular cells. Nutrients that are not water soluble, like lipids, are transported by carrier molecules. For example, fatty acids are transported throughout the body by a protein called albumin.